1. Field of the Invention
This invention relates to a magnetoresistance effect type head to be used as a reproducing head for a magnetic recording and a separate recording-reproducing type magnetic head using the magnetoresistance effect head.
2. Description of the Related Art
In recent years, high densification of magnetic recording has advanced to the extent of realizing systems of such high levels of recording density as 500 Mb/inch.sup.2 in VTR and 200 Mb/inch.sup.2 in HDD for practical use. The demand for further densification of magnetic recording is steadily increasing in enthusiasm. This trend of the magnetic recording toward higher densification entails the essential task of reducing track width. In the case of a 200 Mb/inch HDD system, for example, a track width is 7 .mu.m and the track-to-track separation is about 2 .mu.m and, therefore, the tolerance of the track width is roughly the distance (2 .mu.m) between the adjacent loops of the track. For the sake of attaining further exaltation of the recording density, it is necessary that the track width should be reduced to below 5 to 6 .mu.m and the tolerance should not be more than 0.5 .mu.m. In order to exalt the density of recording to the level of about 10 Gbits/inch.sup.2, it is expected that the track width would be required to be not more than 1 .mu.m and the tolerance thereof to be roughly 0.1 .mu.m. For the purpose of fulfilling these requirements, the magnetic head requires a marked improvement.
A method for defining such a narrow track-width of heads has been reported, by which magnetic core in air bearing surface is focused ion etched (refer to Japanese Patent Laid-Open Application No. 3-296907). This method, however, is handicapped greatly in the capacity for mass production because the method requires processing of the magnetic heads one by one and the focused ion beam etching technique itself has a very poor throughput, though the method is capable of infallibly producing an accurate track width.
A thin-film magnetic head has been reported (Japanese Patent Laid-Open Application No. 3-205607) which has a magnetic core on the air bearing surface the width of which increases in proportion to the distance from the magnetic gap. This method, however, is incapable of acquiring ample forming accuracy because it requires to impart diverging cross sections to the magnetic cores. It is further disadvantageous that it incurs difficulty during the impartation of an axis of easy magnetization in the direction of track width to the narrowed track and fails to confer ample high-frequency permeability on the track.
As respects the reproducing head for a system of such a high recording density as mentioned above, the magnetoresistance effect type head (hereinafter referred to as "MR head") which utilizes magnetoresistance effect, the phenomenon that the electric resistance of a certain type of magnetic thin film or magnetic multilayer thin film is varied by an external magnetic field, has come to attract attention. Since the MR head is capable of producing a high output even in a system having a low relative speed between a head and a medium, it has been heretofore used mainly in stationary head type tape medium reproducing systems. Since the MR head possesses a high S/N, however, it has come to be adopted recently even for the small HDD which has such a low relative speed as several meters/second in the place of the induction type reproducing head.
FIG. 27 shows one example of the construction of the conventional shield type MR head. A pair of leads 2 are connected severally to the opposite ends of a magnetoresistance effect film 1 made of an anisotropic magnetoresistance effect film, a spin valve film, or a artificial lattice film. They jointly form a magnetoresistance effect element (hereinafter referred to as "MR element") 3. This MR element 3 is placed between insulating films 4 and 5 which form a reproducing magnetic gap. On the outer sides of the insulating films 4 and 5, a pair of upper and lower shield layers 6 and 7 capable of defining linear resolution are respectively disposed. The upper shield layer 7 concurrently serves normally as a lower magnetic core of the magnetic head. On the upper shield layer 7, an upper magnetic core 9 is formed through the medium of an insulating film 8 which forms a recording magnetic gap. These components jointly form a recording magnetic path.
When the shield type MR head constructed as described above is used as a reproducing head, the linear resolution thereof is substantially determined by the length of the upper reproducing magnetic gap (the thickness of the insulating film 5) or the length of the lower reproducing magnetic gap (the thickness of the insulating film 4). In the construction of the conventional MR head, however, for the sake of securing insulation between the lead 2 and the upper shield layer 7, it has been necessary that the insulating film 5 should be formed in a thickness roughly equal to step height of the lead. As a result, it has been extremely difficult to define the high linear resolution to a level of not more than the thickness of the lead 2. In fact, the thickness of the lead 2 is desired to be not less than 0.2 .mu.m for the purpose of enabling the MR element to keep its ratio of change of resistance. Thus, the improvement of the linear resolution to be attained in the shield type MR head has had its own limit.
In the system of such high recording density as a recording density exceeding the order of Gb/inch.sup.2, for example, since the necessary linear resolution is equal to or smaller than the thickness of the lead of the shield type MR head, the shield type MR head of the conventional construction described above is incapable of attaining this high linear resolution. Under the circumstances, the desirability of realizing a shield type MR head possessing such a high linear resolution as is suitable for a system of high recording density exceeding the order of Gb/inch.sup.2 has been finding growing recognition.
Further, in the case of a recording density of 1 Gb/inch.sup.2, for example, the width of the shield layers 6 and 7 is desirably set at a level in the approximate range of from 3 to 5 .mu.m because the track width is about 3 .mu.m. Since the shield layers 6 and 7 have a thickness of about 2 .mu.m, the MR element 3 must be formed on a protruding part measuring approximately 2 .mu.m in height and 3 .mu.m in width. In the case of a greater recording density of 10 Gb/inch.sup.2, it is more sternly necessary that the MR element 3 should be formed on a protruding part approximately measuring 2 .mu.m in height and 1 .mu.m in width. An attempt to restrain the size as of the track width of the MR element of a micron order on a substrate having such a protrusion as mentioned above merely results in seriously degrading the yield of production. If a resist 3 .mu.m in thickness is formed on a substrate having a protruding part roughly 2 .mu.m in height and 2 .mu.m in width and a stripe (remnant) pattern 1 .mu.m in width is formed on the resist, for example, the difference of the width of the MR pattern between on a mask and on a wafer will inevitably amount to -0.3 .mu.m. Thus, the conventional shield type MR head entails the problem of imparting an abrupt jog to the substrate of the MR element and rendering accurate regulation of the track width of the MR element no longer practicable when an attempt is made to improve the recording density as described above.
When the recording head is formed on the shield type MR head which is constructed as described above, the magnetic gap of the recording head is such that the linearity thereof depends on the thickness of the lead 2 of the MR element 3 as clearly remarked from FIG. 27. The lead 2 in this case is generally formed by the lift-off method which inflicts only slight damage to the MR element 3. The read 2 which is formed by this lift-off method forms projections in the edge parts at a certain degree of probability even when a reversely tapered resist is used. As a result, the yield of production is degraded by the phenomenon of shortening between the leads and the shield when the projections go to narrow the gap between the shield and the lead. Indeed, the degradation of the yield by the shortening can be prevented to a certain extent by decreasing the thickness of the lead 2. The lead 2, however, does not tolerate a generous decrease of thickness because the decrease of thickness of the lead 2 results in an increase of resistance and a substantial decrease of the ratio of change of resistance.
Specifically, regarding the layout of the lead 2, the practice of disposing the lead 2 in such a manner that the area in which the shield 7 and the lead 2 overlap each other may be decreased to the fullest possible extent as shown in FIG. 28 is followed for the purpose of precluding the shortening between the shield and the lead. FIG. 29 shows the relation between the ratio of change of resistance of the MR element and the variation of the thickness of the lead 2 as determined with respect to varied track widths (T.sub.W) in the construction having the lead 2 disposed as described above. It is clearly noted from FIG. 29 that the dispersion of the specific resistance of the lead 2 increases and, as a result, the ratio of change of resistance abruptly decreases when the thickness of the lead 2 decreases below about 0.4 .mu.m. In order to keep the ratio of change of resistance from decreasing extremely, therefore, it is necessary that the thickness of the lead should be not less than about 0.4 .mu.m, and not less than about 0.2 .mu.m at least.
In the shield type MR head of the conventional construction, the linearity of the recording magnetic gap depends on the thickness of the lead as described above. If the thickness of the lead does not decrease in proportion as the length of the recording magnetic gap decreases as expected in the future, therefore, the linearity of the recording magnetic gap will be degraded more seriously by the difference of level due to the thickness of the lead. With such a track width as the maximum of 5 .mu.m, therefore, the off-track characteristic will be degraded to a great extent. As a result, a heavy azimuth loss is suffered to occur when the MR element is operated for reproduction. In actuality, the degradation of the linearity of the recording magnetic gap which occurs as described above poses a problem when the recording magnetic gap is formed in a size roughly not more than 10 times the thickness of the lead.